Film formation method

Abstract

To provide a film deposition method with excellent mass-production capabilities. [Solution] A method for forming a film using a metal complex represented by the following formula (1). TIFF2026050269000018.tif56165

Description

Technical Field

[0001] The present invention relates to a film forming method.

Background Art

[0002] Thin films of insulator metal oxides, conductor metal oxides, and semiconductor metal oxides (also referred to as oxide semiconductors) are used in various products including semiconductor devices. In particular, as a next-generation switching element capable of realizing high breakdown voltage, low loss, and high heat resistance, semiconductor devices using gallium oxide (Ga2O3) with a large bandgap have attracted attention, and their application to power semiconductor devices such as inverters is expected. Moreover, application as a light-emitting and light-receiving device such as an LED or a sensor is also expected due to its wide bandgap.

[0003] In recent years, p-type gallium oxide-based semiconductors have been studied. For example, Patent Document 1 describes that when a β-Ga2O3-based crystal is formed by the FZ method using MgO (p-type dopant source), a substrate showing p-type conductivity can be obtained.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a film forming method excellent in mass productivity.

Means for Solving the Problems

[0006] In order to solve the above problems, in one aspect of the present invention, a film forming method uses a metal complex represented by the following formula (1).

Chemical Formula

[0007] The film-forming method of the present invention is excellent in mass productivity. [Brief Description of the Drawings]

[0008] [Figure 1] Figure 1 is a schematic configuration diagram of a film-forming apparatus (mist CVD apparatus) used in the examples. [Figure 2] Figure 2 is the measurement result of FT-IR of the chromium complex used in Example 1. [Modes for Carrying Out the Invention]

[0009] The film-forming method of the present invention is a method for forming a metal-containing film on a substrate, and particularly a method for forming a metal oxide film. More specifically, it is characterized in that a metal complex or an aqueous solution of a metal complex is used for forming the metal oxide film. More specifically, for example, it is a method for forming a metal oxide film using a solution in which a metal complex is dissolved by each of a film-forming method of an atomization method (mist CVD method) and a coating method. The film-forming method of the present invention is excellent in mass productivity. In this specification, "excellent in mass productivity" means that the time required to form a film having a desired thickness is short.

[0010] The metal complex or aqueous solution of the metal complex used in the film formation method of the present invention will be described below. A "metal complex" refers to a compound containing a central metal atom and a ligand that coordinates to the central metal atom.

[0011] The metal complex used in the film formation method of the present invention is a metal complex represented by formula (1), described later. Although we do not wish for a restrictive interpretation, the metal complex has a specific ligand and structure, which results in higher solubility in solution (especially water) than conventional metal complexes. As a result, the concentration of the solution used for film formation can be relatively higher, and thus it is considered to have excellent mass productivity. One or more metal complexes represented by formula (1) can be used.

[0012] The metal complex used in the film-forming method of the present invention exhibits high solubility in aqueous solutions while also showing excellent thermal stability. Aqueous solutions containing such metal complexes are less prone to precipitation during long-term storage, thus exhibiting high quality stability.

[0013] [ka] (In formula (1), R 1 and R 2 Each of these independently represents a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 10 carbon atoms. 3 X represents a group represented by the following formula (1A) or formula (1B). 1 (where n is an integer from 0 to 4, the central metal atom is represented by n.) [ka] (In equations (1A) and (1B), R 1 , R 2 and X 1 R in equation (1) 1 , R 2 and X 1 This is synonymous. (* indicates the bond position.)

[0014] In equations (1), (1A), and (1B), X 1 Of the lines connecting them, solid lines indicate covalent bonds, and dashed lines indicate coordinate bonds.

[0015] In equation (1), multiple R 1 and multiple R 2 These may be the same or different. In equation (1), X 1 If there are multiple X 1 They may be the same or they may be different.

[0016] "Number of carbon atoms" refers to the number of carbon atoms that make up the group. "Hydrogen groups" include "aliphatic hydrocarbon groups" and "aromatic hydrocarbon groups." "Aliphatic hydrocarbon groups" include "chain hydrocarbon groups" and "alicyclic hydrocarbon groups." From another perspective, "aliphatic hydrocarbon groups" include "saturated hydrocarbon groups" and "unsaturated hydrocarbon groups." A "chain hydrocarbon group" is a hydrocarbon group that does not contain a ring structure and is composed only of a chain structure, and includes both linear hydrocarbon groups and branched hydrocarbon groups. An "alicyclic hydrocarbon group" is a hydrocarbon group that contains only an alicyclic ring as its ring structure and does not contain an aromatic ring, and includes both monocyclic and polycyclic alicyclic hydrocarbon groups. However, it is not necessary to be composed only of an alicyclic structure, and it may contain a chain structure as part of it. An "aromatic hydrocarbon group" is a hydrocarbon group that contains an aromatic ring as its ring structure. However, it is not necessary to be composed only of an aromatic ring, and it may contain a chain structure or an alicyclic ring as part of it.

[0017] R 1 and R 2 Examples of hydrocarbon groups having 1 to 10 carbon atoms, represented by , include chain hydrocarbon groups having 1 to 20 carbon atoms, alicyclic hydrocarbon groups having 3 to 10 carbon atoms, and aromatic hydrocarbon groups having 6 to 10 carbon atoms.

[0018] Examples of chain hydrocarbon groups having 1 to 10 carbon atoms include methyl, ethyl, and n-propyl groups, as well as alkyl groups such as isopropyl, n-butyl, isobutyl, t-butyl, n-pentyl, and n-hexyl groups. Examples of alicyclic hydrocarbon groups having 3 to 10 carbon atoms include cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups. Examples of aromatic hydrocarbon groups having 6 to 10 carbon atoms include aryl groups such as phenyl and tolyl groups.

[0019] R 1 and R 2 The hydrocarbon group having 1 to 10 carbon atoms represented by is preferably an alkyl group having 1 to 6 carbon atoms, a phenyl group, or a tolyl group, with an alkyl group having 1 to 6 carbon atoms being more preferred. From the viewpoint of achieving both solubility and heat resistance, a methyl group or an ethyl group is even more preferred, with a methyl group being particularly preferred.

[0020] X 1 The valency of the central metal atom is usually trivalent. 1 The central metal atom preferably includes a d-block metal, a group 13 metal, or a group 14 metal of the periodic table; more preferably includes a group 4 metal, a group 6 metal, a group 9 metal, a group 13 metal, or a group 14 metal; even more preferably includes a group 6 metal, a group 9 metal, or a group 13 metal; and even more preferably includes a group 6 metal. In this invention, the central metal atom may also be a metalloid atom.

[0021] Note that "periodic table" refers to the periodic table defined by the International Union of Pure and Applied Chemistry (IUPAC). "d block" refers to elements that have electrons filling the 3d, 4d, 5d, and 6d orbitals.

[0022] "Group 4 metals" are not particularly limited as long as they are Group 4 metals of the periodic table, and examples include titanium (Ti), zirconium (Zr), hafnium (Hf), or two or more of these metals, with titanium being preferred. "Group 6 metals" are not particularly limited as long as they are Group 6 metals of the periodic table, and examples include chromium (Cr), molybdenum (Mo), tungsten (W), or two or more of these metals, with chromium being preferred. "Group 9 metals" are not particularly limited as long as they are Group 9 metals of the periodic table, and examples include iridium (Ir), cobalt (Co), rhodium (Rh), or two or more of these metals, with rhodium or iridium being preferred. "Group 13 metals" are not particularly limited as long as they are Group 13 metals of the periodic table, and examples include aluminum (Al), gallium (Ga), indium (In), thallium (Tl), or two or more of these metals, with gallium or indium being preferred. The term "Group 14 metal" is not particularly limited as long as it is a Group 14 metal of the periodic table. Examples include germanium (Ge), tin (Sn), lead (Pb), or two or more of these metals, with germanium being preferred.

[0023] X 1 The central metal atom can be, specifically, a metal atom selected from, for example, gallium (Ga), iridium (Ir), indium (In), rhodium (Rh), aluminum (Al), gold (Au), silver (Ag), platinum (Pt), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), palladium (Pd), cobalt (Co), ruthenium (Ru), chromium (Cr), molybdenum (Mo), tungsten (W), tantalum (Ta), zinc (Zn), lead (Pb), rhenium (Re), titanium (Ti), tin (Sn), arsenic (As), germanium (Ge), and zirconium (Zr).

[0024] X 1The central metal atom is preferably selected from gallium (Ga), iridium (Ir), indium (In), rhodium (Rh), chromium (Cr), titanium, and germanium, from the viewpoint of reactivity, availability, etc., and chromium (Cr) atoms are particularly preferred due to their solubility in aqueous solutions, etc.

[0025] n may also be 4. It is also preferable that the metal complex includes a compound in formula (1) where n is 4.

[0026] The metal complex represented by formula (1) above preferably includes the metal complex represented by the following formula (2).

[0027] [ka]

[0028] In equation (2), solid lines represent covalent bonds to the chromium atom (Cr), while dashed lines represent coordinate bonds.

[0029] The metal complex represented by formula (1) can be synthesized, for example, by reacting a metal halide compound such as chromium trichloride with acetylacetonate in the presence of a water-soluble base compound such as ammonia, trimethylammonium hydroxide (TMAH), or urea, and a water-soluble acid compound such as hydrochloric acid.

[0030] The metal complex represented by formula (1) may form salts with chloride ions, cyanate ions, etc., in solution (especially in aqueous solutions). Furthermore, the metal complex represented by formula (1) may exist as a hydrate containing water molecules. Therefore, in the film formation method of the present invention, the metal complex represented by formula (3) below may be used together with the metal complex represented by formula (1). In formula (3) below, Z ― The counter anion represented by is determined by the reagent used in the neutralization treatment when synthesizing the metal complex represented by formula (1). For example, when hydrochloric acid is used, the counterion is the chloride ion (Cl -) may occur, and when using cyanic acid, the counterion is the cyanate ion (NCO - ) This may occur.

[0031] [ka]

[0032] (In formula (3), R 4 and R 5 Each of these independently represents a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 10 carbon atoms. 2 Z indicates the central metal atom. - (This indicates chloride ions or cyanate ions.)

[0033] In equation (3), multiple R 4 and multiple R 5 These may be the same or different. R in equation (3) 4 and R 5 The specific form and preferred form of are R in formula (1). 1 and R 2 It is similar to the specific form and preferred form of X. 2 It is preferable that it contains chromium atoms (Cr), and more preferably that it is chromium atoms (Cr). Usually, R 4 and R 5 R 1 and R 2 It is of the same kind as X. Also, usually, X 2 X 1 It is of the same kind.

[0034] As the metal complex represented by formula (3) above, the metal complex represented by the following formula (3-1) is preferred. [ka]

[0035] The metal complex represented by formula (1) is preferably used in the form of an aqueous solution. Such an aqueous solution of the metal complex contains the metal complex represented by formula (1) and an aqueous solvent. The aqueous solution of the metal complex may further contain the metal complex represented by formula (3). The aqueous solution of the metal complex may further contain other metal complexes, and may further contain other components other than the metal complex and the aqueous solvent. The aqueous solution of the metal complex may contain two or more metal atoms.

[0036] The concentration of the central metal atom of the metal complex in the aqueous solution of the metal complex is preferably 0.002 mol / L or more and 0.2 mol / L or less, more preferably 0.005 mol / L or more and 0.1 mol / L or less, and even more preferably 0.007 mol / L or more and 0.03 mol / L or less. The aqueous solution of the metal complex may be the raw material solution or coating solution described later.

[0037] Aqueous solvents refer to (1) water, or (2) a mixed solvent containing water and an organic solvent, with water as the main component. "With water as the main component" means that the water content in the aqueous solvent is 50% by mass or more.

[0038] The organic solvent is not particularly limited as long as it is miscible with water, and examples include lower alcohols such as methanol, ethanol, and isopropanol.

[0039] The aqueous solvent is preferably substantially free of organic solvents, and more preferably completely free of them. "Substantially free of organic solvents" means that the composition may contain an amount of organic solvent that does not cause flammability problems.

[0040] The content of the organic solvent in the aqueous solvent is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably 0% by mass, relative to the total amount of the aqueous solvent.

[0041] In other words, the water content in the aqueous solvent is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, even more preferably 99.9% by mass, and particularly preferably 100% by mass, relative to the total amount of the aqueous solvent.

[0042] The pH of the metal complex aqueous solution is preferably between 4.0 and 7.5. A pH of 4.0 or higher suppresses the decrease in solubility due to ligand exchange reactions of the metal complex in the aqueous solution. A pH of 7.5 or lower facilitates the formation of thin films using the metal complex aqueous solution.

[0043] Next, a film formation method using the metal complex of the present invention will be described. In this film formation method, it is preferable to form a metal oxide film using the metal complex as a raw material. The formed metal oxide film may contain an oxide semiconductor or a crystalline oxide semiconductor. In this film formation method, it is preferable that the metal complex is contained in the liquid raw material. That is, it is preferable that the film formation method uses a liquid containing the metal complex as a raw material. This liquid raw material may be a raw material solution or coating solution described later. The liquid raw material may also be the aforementioned aqueous solution of the metal complex.

[0044] In one embodiment of the present invention, the raw material preferably contains chromium. The chromium is preferably included in a dissolved state in the liquid raw material. The chromium is preferably included as the central metal atom of the metal complex represented by formula (1). The raw material may contain one or more metal atoms.

[0045] In one embodiment of the present invention, the raw materials may include, for example, gallium. It is preferable that the gallium is included in a dissolved state in the liquid raw materials. Gallium may be included, for example, as the central metal atom of the metal complex represented by formula (1), as the central metal atom of another metal complex, or in the form of other salts, etc. The raw materials may also include atoms that become dopants (p-type dopants or n-type dopants). The dopants may also be included as the central metal atom of the metal complex represented by formula (1), as the central metal atom of another metal complex, or in the form of other salts, etc. The raw materials may further include other components.

[0046] In one embodiment of the present invention, if the raw material includes a first metal atom and a second metal atom as multiple types of metals, the lower limit of the atomic ratio of the first metal atom to the second metal atom (first metal atom / second metal atom) may be 1 / 99, or it may be 5 / 95, 10 / 90, 20 / 80, 30 / 70, 40 / 60, 50 / 50, 60 / 40, 70 / 30, 80 / 20, 90 / 10, 95 / 5, or 99 / 1. The upper limit of the atomic ratio of the first metal atom to the second metal atom (first metal atom / second metal atom) may be 99 / 1, or it may be 95 / 5, 90 / 10, 80 / 20, 70 / 30, 60 / 40, 50 / 50, 40 / 60, 30 / 70, 20 / 80, 10 / 90, 5 / 95, or 1 / 99. By adjusting the atomic ratio of the first metal atom to the second metal atom, the physical properties and deposition rate of the resulting metal oxide film can be adjusted. The first metal atom is preferably a metal from Group 6 of the periodic table, with chromium being more preferred. The second metal atom is preferably a metal from Group 13 of the periodic table, with gallium being more preferred.

[0047] Film formation methods include atomization (mist CVD) and coating.

[0048] <Atomization method (mist CVD method)> The atomization method (mist CVD method) uses, for example, the film deposition apparatus shown in Figure 1. The mist CVD apparatus 1 shown in Figure 1 comprises a carrier gas source 2a for supplying carrier gas, a flow control valve 3a for adjusting the flow rate of carrier gas discharged from the carrier gas source 2a, a carrier gas (dilution gas) source 2b for supplying carrier gas (dilution gas), a flow control valve 3b for adjusting the flow rate of carrier gas (dilution gas) discharged from the carrier gas (dilution gas) source 2b, a mist generation source 4 containing a precursor solution, a raw material solution 4a, a container 5 for water 5a, an ultrasonic transducer 6 attached to the bottom of the container 5, a film deposition chamber 7, a supply pipe 9 connecting the mist generation source 4 to the film deposition chamber 7, a hot plate 8 installed inside the film deposition chamber 7, and an exhaust port 11 for discharging atomized droplets and exhaust gas after the thermal reaction. A substrate 10 is placed on the hot plate 8.

[0049] The atomization method (mist CVD method) comprises, for example, a step of atomizing or dropletizing a liquid containing the metal complex (atomization / dropletization step), a step of transporting the obtained mist or droplets to a substrate using a carrier gas (transportation step), and a step of forming a metal oxide film on the substrate by thermally reacting the mist or droplets near the substrate (film formation step). According to the mist CVD method, a metal oxide film with excellent semiconductor properties and surface smoothness can be obtained.

[0050] (Atomization / dropletization process) In the atomization / droplet formation process, the liquid (raw material solution) containing the metal complex is atomized or dropletized. The atomizing or droplet formation means for the raw material solution is not particularly limited as long as it can atomize or dropletize the raw material solution, and any known means may be used. However, in the present invention, an atomizing or droplet formation means using ultrasound is preferred. The mist or droplets obtained using ultrasound are preferred because they have zero initial velocity and float in the air. For example, they are very suitable because they can be transported as a gas floating in space rather than being sprayed like a spray, so there is no damage due to collision energy. The mist particle size or droplet size is not particularly limited and may be several millimeters in size, but is preferably 50 μm or less, and more preferably 100 nm to 10 μm.

[0051] (Raw material solution) The raw material solution contains a metal complex represented by formula (1) above, and is not particularly limited as long as it can be atomized or dropletized, and may contain inorganic materials or organic materials. In the present invention, the raw material solution may contain metal in the form of a complex other than the metal complex or in the form of a salt. Examples of other complex forms include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of salt forms include organometallic salts (e.g., metal acetates, metal oxalates, metal citric acids, etc.), metal sulfide salts, metal nitrate salts, metal phosphorylated salts, and metal halide salts (e.g., metal chloride salts, metal bromide salts, metal iodide salts, etc.).

[0052] Furthermore, it is preferable to mix additives such as hydrohalic acid and oxidizing agents into the raw material solution. Examples of hydrohalic acid include hydrobromic acid, hydrochloric acid, and hydroiodic acid, but hydrobromic acid or hydrochloric acid are preferred, and hydrochloric acid is particularly preferred, because they yield a better quality film. Examples of oxidizing agents include peroxides such as hydrogen peroxide (H2O2), sodium peroxide (Na2O2), barium peroxide (BaO2), and benzoyl peroxide (C6H5CO)2O2, as well as organic oxides such as hypochlorous acid (HClO), perchloric acid, nitric acid, ozonated water, peracetic acid, and nitrobenzene. When the additive is hydrochloric acid, the content of hydrochloric acid in the raw material solution is preferably 1 to 20% by mass, and more preferably 3 to 10% by mass.

[0053] The raw material solution may contain a dopant. By including a dopant in the raw material solution, doping can be performed effectively. The dopant is not particularly limited as long as it does not hinder the objective of the present invention. Examples of the dopant include p-type dopants such as Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Tl, Pb, N, and P. The concentration of the dopant is usually about 1 × 10⁻⁶. 16 / cm 3 ~1 × 10 22 / cm 3 Alternatively, the concentration of the dopant may be set to, for example, approximately 1 × 10⁻⁶. 17 / cm 3 The following low concentrations may also be used. Furthermore, in this invention, the dopant is approximately 1 × 10⁻⁶ 20 / cm 3 It may be included at the above high concentrations.

[0054] The solvent in the raw material solution may be an inorganic solvent such as water, an organic solvent such as alcohol, or a mixed solvent of an inorganic solvent and an organic solvent. In the present invention, it is preferable that the solvent contains water, more preferably that it is water or a mixed solvent of water and alcohol, and even more preferably that it is water.

[0055] (Conveying process) In the transport process, the mist or droplets obtained in the atomization / dropletization process are transported to the substrate using a carrier gas. The type of carrier gas is not particularly limited as long as it does not hinder the objective of the present invention, and examples include inert gases such as oxygen, ozone, nitrogen, and argon, or reducing gases such as hydrogen gas and foaming gas. Among these, oxygen gas, ozone gas, or nitrogen gas are preferred as carrier gases, and nitrogen gas is more preferred. In addition, there may be one type of carrier gas, or there may be two or more types, and a dilution gas with a changed carrier gas concentration (e.g., a 10-fold dilution gas) may be used as a second carrier gas. Furthermore, there may be two or more locations for supplying the carrier gas, not just one. In addition, the flow rate of the carrier gas is not particularly limited, but it is preferably 0.01 L / min to 20 L / min, and more preferably 0.1 to 10 L / min.

[0056] The substrate is not particularly limited as long as it can support the metal oxide film, but it is preferable that it has a corundum structure. The material of the substrate may be a known substrate, and may be an organic compound or an inorganic compound. Suitable examples of substrate materials include sapphire, α-type gallium oxide, and other metal oxides having a corundum structure. It is preferable that at least a portion of the substrate, including the crystal growth surface, contains gallium as the main component. "Main component" means that, in terms of atomic ratio, it is preferably present in 50% or more, more preferably 70% or more, and even more preferably 90% or more of the total components of the substrate, and may be 100%.

[0057] The shape of the substrate can be any shape and is effective for any shape, such as a flat plate or disc (hereinafter also referred to as "substrate"), a fibrous shape, a rod shape, a cylindrical shape, a prismatic shape, a tubular shape, a spiral shape, a spherical shape, a ring shape, etc., but in the present invention, a substrate is preferred. The thickness of the substrate is not particularly limited in the present invention.

[0058] A substrate having a corundum structure is preferred as the substrate. Specifically, examples include a sapphire substrate and an α-type gallium oxide substrate. Here, the main surface of the substrate is preferably a surface inclined from the c-plane, and more preferably the m-plane.

[0059] (Film forming process) In the film formation process, the mist or droplets transported in the transport process are subjected to a thermal reaction near the substrate to form a metal oxide film on the substrate. The metal oxide film is formed by the formation of metal oxide crystals or mixed crystals through this thermal reaction. The thermal reaction temperature is preferably 900°C or lower, and more preferably less than 600°C. In the film formation method of the present invention, a metal oxide film can be formed even at a relatively low temperature of less than 600°C. The lower limit of the thermal reaction temperature may be, for example, 300°C, 400°C, or 500°C. Furthermore, the film formation process may be carried out under any atmosphere, such as vacuum, non-oxygen atmosphere, reducing gas atmosphere, or oxidizing atmosphere, as long as it does not hinder the objective of the present invention, and may also be carried out under any conditions, such as atmospheric pressure, pressurized, or reduced pressure. However, in the present invention, it is preferably carried out under an oxidizing atmosphere, preferably under atmospheric pressure, and more preferably under both an oxidizing atmosphere and atmospheric pressure. The "oxidizing atmosphere" is not particularly limited as long as it is an atmosphere in which metal oxide crystals or mixed crystals can be formed, and is sufficient if oxygen or an oxygen-containing compound is present. For example, an oxidizing atmosphere can be created by using an atmosphere containing 1% or more oxygen in an inert gas, using an oxygen-containing carrier gas, or using an oxidizing agent. The film thickness can be set by adjusting the film formation time. In the present invention, it is preferably 20 nm or more, more preferably 30 nm or more, and may be 40 nm or more, 100 nm or more, or 1 μm or more. There is no particular upper limit to the film thickness, but it is preferably 1 mm, and more preferably 100 μm. In addition, in the present invention, the metal complex may be subjected to this process with a p-type dopant included, and the metal oxide having the corundum structure may be p-doped. Examples of the p-type dopant include Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Tl, Pb, N, P, and two or more of these elements. In addition, in the present invention, the metal oxide film obtained in this step may be subjected to annealing treatment.

[0060] <Application Method> The coating method involves applying a liquid containing a metal complex onto a substrate and drying it to form a metal oxide film.

[0061] The liquid containing the metal complex (coating solution) is the main compound raw material for forming a metal oxide film on the substrate. The content of the metal complex in the liquid is preferably in the range of 1 to 30% by mass, and more preferably 5 to 20% by mass. If the content is higher than 30% by mass, the metal complex is more likely to precipitate, which can reduce the stability of the coating solution, or the resulting metal oxide film may become too thick, leading to cracking.

[0062] If necessary, a small amount of one or more of the following may be added to the coating solution: an organotin compound, an organotin compound, or an organozinc compound. Furthermore, an organic binder may be added to the coating solution if necessary. Adding an organic binder improves the wettability to the substrate and simultaneously adjusts the viscosity of the coating solution. The organic binder is preferably made of a material that burns or decomposes during heat treatment, and effective such materials include cellulose derivatives and acrylic resins.

[0063] Examples of cellulose derivatives used in organic binders include methylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, carboxyethylcellulose, carboxyethylmethylcellulose, and nitrocellulose. Among these, hydroxypropylcellulose (hereinafter sometimes referred to as "HPC") is preferred.

[0064] Furthermore, many types of cellulose derivatives and acrylic resins with different molecular weights are commercially available. For example, HPC has high molecular weight, medium molecular weight, and low molecular weight types, and the higher the molecular weight, the higher the viscosity of the metal complex aqueous solution containing the metal complex blended as a binder. The selection of the molecular weight type and the determination of the blending amount need to be optimized as needed, depending on the applicability of the coating solution, the coating method, and the coating film thickness.

[0065] Using the aforementioned HPC, sufficient wettability can usually be obtained with a content of 5% by mass or less, while simultaneously allowing for significant viscosity adjustment. Furthermore, the combustion start temperature of HPC is around 300°C, and combustion occurs when the heat treatment is performed at a heating temperature of 300°C or higher, preferably 350°C or higher. Therefore, it does not inhibit the grain growth of the generated conductive particles, and a metal oxide film with good conductivity can be produced. If the HPC content exceeds 5% by mass, it tends to become gel-like and remain in the coating liquid, forming an extremely porous metal oxide film, which severely impairs transparency and conductivity.

[0066] Here, if ethylcellulose is used as a cellulose derivative, for example, instead of HPC, the viscosity of the coating solution can usually be set lower than when HPC is used. However, in screen printing methods and the like, where a high viscosity coating solution is preferred, the pattern printability is slightly reduced.

[0067] The solvent of the coating solution may be an inorganic solvent such as water, an organic solvent such as alcohol, or a mixed solvent of an inorganic solvent and an organic solvent. In the present invention, it is preferable that the solvent contains water, more preferably that it is water or a mixed solvent of water and alcohol, and even more preferably that it is water.

[0068] The aforementioned coating solution may contain organic solvents other than the water and alcohol mentioned above. The solvent added to lower the viscosity of the coating solution or improve its applicability should be compatible with solutions containing various organometallic compounds and cellulose derivatives or acrylic resins. Other solvents include, for example, ketone solvents such as acetone, methyl ethyl ketone (MEK), methyl propyl ketone, methyl isobutyl ketone (MIBK), cyclohexanone, and isophorone; ethyl acetate, butyl acetate, amyl formate, isoamyl acetate, butyl propionate, isopropyl butyrate, ethyl butyrate, butyl butyrate, methyl lactate, and ethyl lactate. Methyl oxyacetate, ethyl oxyacetate, butyl oxyacetate, methyl methoxyacetate, ethyl methoxyacetate, butyl methoxyacetate, methyl ethoxyacetate, ethyl ethoxyacetate, methyl 3-oxypropionate, ethyl 3-oxypropionate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, methyl 3-ethoxypropionate, ethyl 3-ethoxypropionate, methyl 2-oxypropionate, ethyl 2-oxypropionate, propyl 2-oxypropionate, methyl 2-methoxypropionate, methyl 2-methyl 2-meth Ester solvents such as ethyl xypropionate, propyl 2-methoxypropionate, methyl 2-ethoxypropionate, ethyl 2-ethoxypropionate, methyl 2-oxy-2-methylpropionate, ethyl 2-oxy-2-methylpropionate, methyl 2-methoxy-2-methylpropionate, ethyl 2-ethoxy-2-methylpropionate, methyl pyruvate, ethyl pyruvate, propyl pyruvate, methyl acetoacetate, ethyl acetoacetate, methyl 2-oxobutanoate, ethyl 2-oxobutanoate, and ethylene glycol mono Methyl ether (MCS), ethylene glycol monoethyl ether (ECS), ethylene glycol isopropyl ether (IPC), ethylene glycol monobutyl ether (BCS), ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol methyl ether (PGM), propylene glycol ethyl ether (PE), propylene glycol methyl ether acetate (PGM-AC), propylene glycol ethyl ether acetate (PE-AC),Examples of glycol derivatives include, but are not limited to, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and dipropylene glycol monobutyl ether; benzene derivatives such as toluene, xylene, mesitylene, and dodecylbenzene; formamide (FA), N-methylformamide, dimethylformamide (DMF), dimethylacetamide, dimethyl sulfoxide (DMSO); ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butylene glycol, pentamethylene glycol, 1,3-octylene glycol, tetrahydrofuran (THF), chloroform, mineral spirits, terpineol, and several mixtures thereof.

[0069] The viscosity of the coating solution can be adjusted according to the molecular weight and content of the organic binder and the type of solvent, so it can be adjusted to a viscosity suitable for each of the various coating methods, such as inkjet printing, screen printing, gravure printing, offset printing, flexographic printing, dispenser printing, slit coating, die coating, doctor blade coating, wire bar coating, spin coating, and spray coating.

[0070] High-viscosity coating solutions (approximately 5,000 to 50,000 mPa·s) can be prepared by including 5% by mass or less, preferably 2 to 4% by mass, of a high-molecular-weight organic binder. Low-viscosity solutions (approximately 5 to 500 mPa·s) can be prepared by including 5% by mass or less, preferably 0.1 to 2% by mass, of a low-molecular-weight organic binder and diluting it with a low-viscosity diluent. Medium-viscosity coating solutions (500 to 5,000 mPa·s) can be prepared by mixing a high-viscosity coating solution with a low-viscosity coating solution.

[0071] The coating method comprises, more specifically, a step of applying the coating liquid onto a substrate to form a coating film (coating step), a step of drying the coating film to form a dried coating film (drying step), and a step of heat-treating the dried coating film in an oxygen-containing atmosphere with a low dew point temperature to form an inorganic film (heat treatment step).

[0072] Various methods for coating onto a substrate include inkjet printing, screen printing, gravure printing, offset printing, flexographic printing, dispenser printing, slit coating, die coating, doctor blade coating, wire bar coating, spin coating, and spray coating.

[0073] These coatings should preferably be applied in a clean environment with controlled temperature and humidity, such as a cleanroom. Typical temperatures are room temperature (around 25°C) and humidity between 40-60% RH.

[0074] The aforementioned substrate is described in the section on atomization (mist CVD method) above.

[0075] In the drying process, the substrate coated with the coating solution is usually held in the air at 80 to 180°C for 1 to 30 minutes, preferably 2 to 10 minutes, to dry the coating film and produce a dried coating film.

[0076] The drying conditions (drying temperature, drying time) can be appropriately selected depending on the type of substrate used, the coating thickness, etc., and are not limited to the aforementioned drying conditions. However, considering productivity, it is desirable to shorten the drying time to the minimum necessary so as not to deteriorate the quality of the resulting dried coating film.

[0077] Furthermore, the drying temperature must be below the heat resistance temperature of the substrate used. For example, with the PEN film mentioned above, the temperature needs to be set to around 200°C or below (depending on the drying time). If necessary, vacuum drying (ultimate pressure: usually 1 kPa or less) can be applied instead of drying in the air. In vacuum drying, the applied solvent is forcibly removed under reduced pressure, allowing for drying at lower temperatures compared to drying in the air. This is useful when using substrates made of materials with poor heat resistance or solvent resistance.

[0078] The prepared dried coating film is obtained by volatilizing and removing the aforementioned organic solvent from the coating solution, and is composed of organic components such as the organometallic compound (organoindium compound, organotin compound, organozinc compound, which may be added in small amounts as needed), and an organic binder.

[0079] In the heat treatment process, the dried coating film produced in the drying process is heat-treated in an oxygen-containing atmosphere with a low dew point temperature to mineralize the organometallic compound in the dried coating film, or the organometallic compound including a small amount of added organometallic compound, and organic components such as organic binders, by thermal decomposition and combustion (oxidation), thereby forming a dense inorganic film (a metal oxide film as a layer of densely packed metal oxide nanoparticles) consisting mainly of inorganic components (metal oxides).

[0080] In other words, as the heating temperature increases during the heating process, the organometallic compounds in the dried coating film (including those containing small amounts of organometallic compounds) are gradually thermally decomposed and burned (oxidized), first resulting in a conversion to an amorphous metal oxide (here, this refers to a state of very fine particles with a crystallite size of less than 3 nm, as determined by X-ray diffraction), so-called mineralization. Subsequently, if the heating temperature rises further and exceeds the usual range of 300-330°C, or if the heating time is extended even if the temperature remains within the 300-330°C range, crystallization of the metal oxide occurs, and further crystal growth occurs to become metal oxide nanoparticles, which become the final components of the metal oxide film.

[0081] It should be noted that the temperature range of 300-330°C represents a general temperature range in which mineralization and crystallization are likely to occur. For example, if the heating time is long, mineralization, crystallization, and crystal growth of the metal oxide may occur even at around 270°C. Therefore, the heating temperature in the heat treatment process of the present invention is not limited to 300°C or higher.

[0082] On the other hand, organic binders also gradually undergo thermal decomposition and combustion (oxidation) during the heating process, but are mainly converted into carbon dioxide (CO2) and volatilize into the atmosphere, disappearing from the film (depending on the type of organic binder, for example, the aforementioned HPC almost disappears at around 300-350°C), so ultimately almost none remains in the metal oxide film. It should be noted that a large amount of organic binder remains in the initial stages of the heating process (for example, at a certain stage in the heating process, when heating from room temperature to 300°C), and the organic binder is uniformly interposed between the amorphous metal oxides, suppressing crystallization. However, as the heating process progresses further, the organic binder component gradually disappears, and crystallization of the metal oxide occurs.

[0083] The heat treatment process will be explained in more detail below.

[0084] In the heat treatment process of the dried coating film of the present invention, by first applying an oxygen-containing atmosphere with a low dew point temperature, i.e., a low water vapor content, to the atmosphere during the heating process, the crystallization of metal oxides due to mineralization that occurs in the initial stage of the heat treatment process as described above, and the growth of crystals are suppressed, thereby obtaining the film structure of the metal oxide nanoparticle layer of the present invention in which metal oxide nanoparticles are densely packed. Although the mechanism by which the metal oxide nanoparticles are densely packed is not entirely clear, it can be considered as follows, for example.

[0085] In other words, at least until the point in time when crystallization of the metal oxide occurs due to mineralization during the heating process (the initial stage of the heating process; usually around 300-330°C in this invention), a film structure in which the organic binder is uniformly interposed between the amorphous metal oxides is maintained. This film structure has flexibility due to the action of the organic binder, which is an organic substance, and allows the film to shrink (densify) perpendicular to the substrate. Therefore, when the heating process is carried out by raising the temperature in an air atmosphere with a low dew point temperature, it is presumed that the crystallization of the metal oxide is suppressed up to the heating temperature just before the organic binder disappears (up to about 300-350°C), allowing the aforementioned shrinkable film structure to be maintained, which leads to film densification.

[0086] <Metal oxide film> The metal oxide film obtained by the above-described preferred formation method is industrially useful. The metal oxide film may contain a crystalline oxide semiconductor, for example, with a mobility of 1.0 cm. 2 The semiconductor layer may have a mobility of 3.0 cm² or higher. The mobility refers to the mobility obtained by Hall effect measurement, and the mobility is 3.0 cm². 2 It is preferable that the carrier density of the metal oxide film is 8.0 × 10⁻¹⁰. 20 / cm 3 It is also preferable that the above is true. Here, the carrier density refers to the carrier density in the semiconductor layer obtained by Hall effect measurement. The lower limit of the carrier density is not particularly limited, but is approximately 1.0 × 10⁻⁶. 15 / cm 3 The above is preferable, approximately 1.0 × 10 17 / cm 3 The above is more preferable. In the present invention, by adjusting the type and amount of dopant or the material and content of the mixed crystal, the carrier density can be increased to 1.0 × 10⁻⁶. 15 / cm 3 ~1.0×10 20 / cm 3 It can be easily controlled within that range.

[0087] The metal oxide film preferably contains chromium atoms. The metal oxide film may be, for example, a metal oxide film containing α-Cr2O3, a film mainly containing α-Cr2O3, or a film of α-Cr2O3. "Mainly containing α-Cr2O3" means that the α-Cr2O3 content in the metal oxide film is 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more.

[0088] The metal oxide film may contain multiple types of metal atoms. The metal oxide film may contain mixed crystals. If the metal oxide contains a first metal atom and a second metal atom, the lower limit of the atomic ratio of the first metal atom to the second metal atom (first metal atom / second metal atom) may be 1 / 99, 5 / 95, 10 / 90, 20 / 80, 30 / 70, 40 / 60, 50 / 50, 60 / 40, 70 / 30, 80 / 20, 90 / 10, 95 / 5, or 99 / 1. The upper limit of the atomic ratio (first metal atom / second metal atom) between the first and second metal atoms may be 99 / 1, but may also be 95 / 5, 90 / 10, 80 / 20, 70 / 30, 60 / 40, 50 / 50, 40 / 60, 30 / 70, 20 / 80, 10 / 90, 5 / 95, or 1 / 99. By adjusting the atomic ratio between the first and second metal atoms, the physical properties and deposition rate of the metal oxide film can be adjusted. The first metal atom is preferably a metal from Group 6 of the periodic table, and more preferably chromium. The second metal atom is preferably a metal from Group 13 of the periodic table, and more preferably gallium. The metal oxide may include, for example, a mixed crystal of α-Cr2O3 and α-Ga2O3.

[0089] The metal oxide film is suitably used, for example, as a p-type semiconductor layer by known means. The p-type semiconductor layer may be deposited directly on a substrate, or other layers such as a semiconductor layer different from the p-type semiconductor layer (e.g., an n-type semiconductor layer, an n+-type semiconductor layer, an n--type semiconductor layer, etc.), an insulating layer (including a semi-insulating layer), a buffer layer, or an alignment layer may be laminated on the substrate, and then the p-type semiconductor layer may be deposited on the substrate via the other layers. An alignment layer is a layer provided for the crystal growth of the semiconductor layer laminated thereon. Examples of semiconductor layers and insulating layers include semiconductor layers and insulating layers containing the group 13 metal. Suitable examples of buffer layers and alignment layers include semiconductor layers, insulating layers, or conductive layers containing a corundum structure. Examples of semiconductor layers containing a corundum structure include α-Fe2O3, α-Ga2O3, α-Cr2O3, and α-Al2O3. The metal oxide film of the present invention can also be used as various semiconductor layers (n-type semiconductor layer, n+-type semiconductor layer, n--type semiconductor layer, etc.), insulating layers, buffer layers, and orientation layers, etc.

[0090] Furthermore, it is preferable to form the n-type semiconductor layer before or after the deposition of the p-type semiconductor layer. More specifically, it is preferable that the method for manufacturing the semiconductor device includes a step of stacking at least a p-type semiconductor layer and an n-type semiconductor layer. The means for forming the n-type semiconductor layer are not particularly limited and may be known means, but in the present invention, the mist CVD method is preferred. The n-type semiconductor layer can also be manufactured by the deposition method of the present invention. The n-type semiconductor layer is preferably mainly composed of an oxide semiconductor, and more preferably mainly composed of an oxide semiconductor containing a Group 13 metal of the periodic table (e.g., Al, Ga, In, Tl, etc.). It is also preferable that the n-type semiconductor layer is mainly composed of a crystalline oxide semiconductor, more preferably mainly composed of a crystalline oxide semiconductor containing Ga, and most preferably mainly composed of a crystalline oxide semiconductor having a corundum structure and containing Ga. Furthermore, in the present invention, it is preferable that the difference in lattice constants between the oxide semiconductor, which is the main component of the n-type semiconductor, and the p-type oxide semiconductor is small, as this allows for the formation of a good pn junction. The lattice constant difference is, for example, 1.5% or less, more preferably 1.0% or less, and even more preferably 0.5% or less.

[0091] Here, "lattice constant difference" is defined as the absolute value (%) of the value obtained by subtracting the lattice constant of the p-type oxide semiconductor from the lattice constant of the oxide semiconductor that is the main component of the n-type semiconductor, and then dividing that value by the lattice constant of the p-type oxide semiconductor, multiplying by 100. An example of a case where the lattice constant difference is 1.5% or less is when the p-type oxide semiconductor has a corundum structure, and the oxide semiconductor that is the main component of the n-type semiconductor also has a corundum structure. More preferably, the p-type oxide semiconductor is a single crystal or mixed crystal of Cr2O3, and the oxide semiconductor that is the main component of the n-type semiconductor is a single crystal or mixed crystal of Ga2O3. Note that "main component" means that the oxide semiconductor is preferably present in an atomic ratio of 50% or more, more preferably 70% or more, and even more preferably 90% or more of the total components of the n-type semiconductor layer, and may be 100%. Furthermore, in the present invention, the p-type oxide semiconductor may be a single crystal, a polycrystalline, or the like.

[0092] The metal oxide films obtained by the various metal oxide film formation methods described above can be used in semiconductor devices as semiconductor layers, insulator layers, buffer layers, orientation layers, etc., and are particularly useful in power devices. By using the metal oxide film in a semiconductor device, roughness scattering can be suppressed, and the channel mobility of the semiconductor device can be improved. Semiconductor devices can be classified into horizontal devices, where electrodes are formed on one side of the semiconductor layer, and vertical devices, where electrodes are formed on both the front and back sides of the semiconductor layer. In the present invention, the metal oxide film can be suitably used in both horizontal and vertical devices, but it is especially preferable to use it in vertical devices. Examples of the semiconductor device include Schottky barrier diodes (SBDs), metal-semiconductor field-effect transistors (MESFETs), high electron-mobility transistors (HEMTs), metal oxide film semiconductor field-effect transistors (MOSFETs), electrostatic induction transistors (SITs), junction field-effect transistors (JFETs), insulated gate bipolar transistors (IGBTs), and light-emitting diodes. The metal oxide film can also be used in devices other than semiconductor devices. [Examples]

[0093] The present invention will be described in detail below based on examples. The present invention is not limited to these examples.

[0094] [Synthesis of chromium complexes] (Synthesis Example 1) A metal complex represented by the following formula (2) (hereinafter also referred to as the "chromium complex") was synthesized according to the method described below.

[0095] [ka]

[0096] 0.2 mol of chromium trichloride was dissolved in ultrapure water. This solution was heated to 60°C, and 1.5 mol of acetylacetonate was added dropwise. The resulting mixed solution was neutralized by adding alkaline aqueous solution and acidic aqueous solution to bring the pH to approximately 7. The mixture was stirred overnight at a temperature between 80°C and 110°C. The reaction solution was then filtered, and the reaction product was extracted by adding an organic solvent to the filtrate. The solvent in the extracted organic layer was removed by distillation. The residue was purified by adding an organic solvent to obtain chromium complex 1. The yield was 10% by mass. The structure was identified and confirmed by LC-Mass spectroscopy (Thermo Fisher Scientific "UltiMate3000") and FT-IR (Bruker "VERTEX70v"). Figure 2 shows the FT-IR of the obtained compound. The following peaks originating from the ligand acetylacetonate were confirmed: 1570~1580 cm⁻¹ -1 (CO stretching vibration), 1520~1530cm -1 (CCC stretching vibration), 1420~1430cm -1 (CH3 stretching vibration), 1380~1400cm -1 (OCCCO stretch vibration), 1280~1290cm -1 (CCC stretching vibration).

[0097] Based on the above identification results, it was further confirmed that metal complexes represented by the following formulas (2-1), (2-2), and (2-3) were present as by-products.

[0098] [ka]

[0099] [Film deposition by mist CVD method] In this example, film deposition was performed using the mist CVD method.

[0100] (Example 1) 1. Manufacturing equipment The mist CVD apparatus 1 (cold wall type) shown in Figure 1 above was used for film deposition by the mist CVD method in the example. However, since no diluent gas was used, the carrier gas (diluent gas) source 2b and the flow control valve 3b for adjusting the flow rate of the carrier gas (diluent gas) were not used.

[0101] 2. Preparation of raw material solution An aqueous solution containing the chromium complex represented by formula (2) obtained in Synthesis Example 1 (chromium (Cr) concentration 0.05 mol / L) was mixed with pure water to prepare an aqueous solution with a chromium (Cr) concentration of 0.01 mol / L, which was used as the raw material solution.

[0102] 3. Preparation for film deposition The raw material solution 4a obtained in step 2 above was placed in the mist generating source 4. Next, an m-plane sapphire substrate was placed on the hot plate 8 as the substrate 10, and the temperature of the hot plate 8 was increased to raise the substrate 10 to 550°C. Next, the flow control valves 3a and 3b were opened, and carrier gas was supplied from the carrier gas source 2a, which is the carrier gas source, into the deposition chamber 7. After the atmosphere in the deposition chamber 7 was sufficiently replaced with the carrier gas, the flow rate of the carrier gas was adjusted to 1.0 L / min. Nitrogen was used as the carrier gas.

[0103] 4.Membrane formation Next, an ultrasonic transducer was vibrated, and the vibrations were transmitted through water 5a to the raw material solution 4a, thereby atomizing the raw material solution 4a and generating atomized droplets. These atomized droplets were transported to the deposition chamber 7 by a carrier gas, and under atmospheric pressure and at a temperature of 550°C, the atomized droplets underwent a thermal reaction on the surface of the substrate 10 to form a film on the substrate 10. The deposition time was 60 minutes. The film thickness was 57 nm.

[0104] The film obtained in step 4 above was identified using an X-ray diffraction apparatus, and it was determined to be an α-Cr2O3 film. Furthermore, the evaluation result for <Evaluation of Mass Producibility> below was "A".

[0105] (Example 2) The film was obtained in the same manner as in Example 1, except that hydrobromic acid was added to a concentration of 10% by mass when preparing the aqueous solution. The film thickness was 50 nm. The obtained film was identified using an X-ray diffraction apparatus, and it was determined to be an α-Cr2O3 film. The evaluation result in the <Evaluation of Mass Producibility> section below was "A".

[0106] (Comparative Example 1) Except for using chromium acetylacetonate instead of the chromium complex shown in formula (2) above, we attempted to carry out the same procedure as in Example 1. However, chromium acetylacetonate did not dissolve in water, and we were unable to prepare an aqueous solution of chromium acetylacetonate at the same concentration as in Example 1 (chromium concentration 0.01 mol / L). Therefore, we conducted the experiment with a system with a lower chromium concentration. Specifically, we used a solution prepared by adding hydrochloric acid to an aqueous solution of chromium acetylacetonate (chromium (Cr) concentration 0.001 mol / L) to a total of 3% by mass as the starting solution. Film deposition was carried out in the same manner as in Example 1, except for the starting solution. The thickness of the obtained film was 5 nm or less. Furthermore, the evaluation result in the <Evaluation of Mass Producibility> below was "C".

[0107] (Example 3) An aqueous solution was prepared by mixing the aqueous solution containing the chromium complex represented by formula (2) obtained in Synthesis Example 1 (chromium (Cr) concentration 0.05 mol / L) with a solution of gallium acetylacetonate (gallium (Ga) concentration 0.01 mol / L) to which hydrochloric acid was added to a total of 3% by mass, thereby obtaining a raw material solution. A film was obtained in the same manner as in Example 1, except that this raw material solution was used. When the obtained film was identified using an X-ray diffraction apparatus, the obtained film was found to be an α-(Cr,Ga)2O3 film. The obtained film was thicker than the film obtained in Example 1, and the evaluation result in the <Evaluation of Mass Producibility> below was "A".

[0108] <Evaluation of mass production capabilities> For Examples 1-3 and Comparative Example 1, the progress of film formation was evaluated using the mist CVD method over a 60-minute film formation time. A thicker film formed in 60 minutes indicates superior mass productivity. The film thickness of the metal oxide obtained after the 60-minute film formation reaction was measured using a spectroscopic ellipsometer (SEMILAB, model SE-2000). If the film thickness was in the range of 40 nm or more, it was considered excellent and given an "A" rating. If the film thickness was in the range of over 10 nm and less than 40 nm, it was considered good and given a rating of "B". If the film thickness was in the range of 10 nm or less, the deposition rate was considered poor and was marked as "C".

[0109] [Film formation by coating method] In this example, film formation was performed by a coating method.

[0110] (Example 4) 1. Preparation of the coating solution The aqueous solution containing the chromium complex used in Example 1 (chromium concentration 0.01 mol / L) was used as the coating solution.

[0111] 2. Preparation of metal oxide films The aforementioned coating solution was spin-coated (1000 rpm × 60 sec) over the entire surface of a sapphire substrate at 25°C and atmospheric pressure, and then dried in air at 150°C for 10 minutes to obtain a dried coating film (film thickness: approximately 300 nm). This coating film was then heat-treated in air at 550°C for 6 hours to obtain a metal oxide film. The evaluation result for the surface roughness of the metal oxide film, as shown below, was "A".

[0112] (Comparative Example 2) A metal oxide film was prepared in the same manner as in Example 4, except that the coating solution was an aqueous solution containing chromium acetylacetonate (chromium concentration 0.001 mol / L) as used in Comparative Example 1. The evaluation result for the surface roughness of the metal oxide film, as shown below, was "C".

[0113] <Evaluation of surface roughness of metal oxide films> The surface roughness (Ra) of the obtained films was observed using an AFM (Scanning Atomic Force Microscope, Bruker Dimension Fastscan / Icon). The following criteria were used for evaluation. Surface roughness values ​​between 1 nm and less than 3 nm were considered excellent and rated "A". Surface roughness values ​​between 3 nm and less than 5 nm were considered good and rated as "B". If the surface roughness value was in the range of 5 nm or more, the surface roughness was considered poor and was graded "C".

[0114] The results from the examples and comparative examples show that the film deposition method of the present invention has a high deposition rate and excellent mass productivity, and the resulting metal oxide film has excellent film quality such as surface smoothness, making it industrially useful.

[0115] <Note> [Section 1] A method for forming a thin film using a metal complex represented by the following formula (1). [ka] (In formula (1), R 1 and R 2 Each of these independently represents a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 10 carbon atoms. 3 X represents a group represented by the following formula (1A) or formula (1B). 1 (where n is an integer from 0 to 4, the central metal atom is represented by n.) [ka] (In equations (1A) and (1B), R 1 , R 2 and X 1 R in equation (1) 1 , R 2 and X 1 This is synonymous. (* indicates the bond position.) [Section 2] The method for forming a film according to item 1, wherein the central metal atom contains a d-block metal of the periodic table, a group 13 metal of the periodic table, or a group 14 metal of the periodic table. [Item 3] The film forming method according to item 1 or item 2, wherein the central metal atom is a chromium atom. [Item 4] The film forming method according to any one of items 1 to 3, wherein the metal complex contains a metal complex represented by the following formula (2). [Chemical formula] [Item 5] The film forming method according to any one of items 1 to 4, further using a metal complex represented by the following formula (3). [Chemical formula] (In formula (3), R 4 and R 5 each independently represent a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 10 carbon atoms. X 2 represents a central metal atom. Z - represents a chloride ion or a cyanate ion.) [Item 6] The film forming method according to any one of items 1 to 5, forming a metal oxide film using the metal complex as a raw material. [Item 7] The film forming method according to item 6, wherein the metal oxide film contains a crystalline oxide semiconductor. [Item 8] The film forming method according to any one of items 1 to 7, supplying the metal complex onto a substrate having a corundum structure. [Item 9] The film forming method according to item 8, wherein at least a part including the crystal growth plane of the substrate contains gallium as a main component. [Item 10] The film forming method according to any one of items 1 to 9, comprising a step of atomizing or dropletizing a liquid containing the metal complex, a step of transporting the obtained mist or droplets to the substrate with a carrier gas, and a step of thermally reacting the mist or droplets in the vicinity of the substrate to form a metal oxide film on the substrate. [Item 11] A method for forming a film according to any one of the above claims 1 to 9, comprising the step of coating a substrate with a liquid containing the metal complex and drying it to form a metal oxide film on the substrate. [Section 12] The film formation method according to any one of the above items 1 to 11, wherein the metal complex is contained in the liquid raw material. [Section 13] The aforementioned raw material is a film-forming method according to any one of the preceding items 1 to 12, comprising gallium. [Section 14] The aforementioned metal complex is contained in the liquid raw material, The aforementioned raw material is a film-forming method according to any one of items 1 to 11, comprising a p-type dopant. [Explanation of Symbols]

[0116] 1. Mist CVD apparatus 2a Carrier gas source 2b Carrier gas (dilution) source 3a Flow control valve 3b Flow control valve 4. Mist source 4a Raw material solution 5 containers 5a water 6. Ultrasonic transducer 7 Deposition chamber 8 Hot plate 9 Supply pipe 10 Base 11 Exhaust vent

Claims

1. A method for forming a thin film using a metal complex represented by the following formula (1). 【Chemistry 1】 (In formula (1), R １ and R ２ Each of these independently represents a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 10 carbon atoms. ３ X represents a group represented by the following formula (1A) or formula (1B). １ (where n is an integer from 0 to 4, the central metal atom is represented by n.) 【Chemistry 2】 (In Formula (1A) and Formula (1B), R １ , R ２ and X １ are synonymous with R １ , R ２ and X １ in Formula (1). * indicates a bonding position.)

2. The method for forming a film according to claim 1, wherein the central metal atom contains a d-block metal of the periodic table, a group 13 metal of the periodic table, or a group 14 metal of the periodic table.

3. The method for forming a film according to claim 1 or claim 2, wherein the central metal atom is a chromium atom.

4. The method for forming a film according to claim 1 or claim 2, wherein the metal complex comprises a metal complex represented by the following formula (2). 【Transformation 3】

5. The method for forming a film according to claim 1 or claim 2, further using a metal complex represented by the following formula (3). 【Chemistry 4】 (In formula (3), R ４ and R ５ Each of these independently represents a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 10 carbon atoms. ２ Z indicates the central metal atom. － (This indicates chloride ions or cyanate ions.)

6. The method for forming a film according to claim 1 or claim 2, wherein a metal oxide film is formed using the aforementioned metal complex as a raw material.

7. The method for forming a film according to claim 6, wherein the metal oxide film includes a crystalline oxide semiconductor.

8. The method for forming a film according to claim 1 or claim 2, wherein the metal complex is supplied onto a substrate having a corundum structure.

9. The method for forming a film according to claim 8, wherein at least a portion of the substrate, including the crystal growth surface, contains gallium as the main component.

10. A method for forming a film according to claim 1 or claim 2, comprising the steps of: atomizing or dropletizing a liquid containing the metal complex; transporting the obtained mist or droplets to a substrate using a carrier gas; and forming a metal oxide film on the substrate by thermally reacting the mist or droplets near the substrate.

11. A method for forming a film according to claim 1 or 2, comprising the step of coating a substrate with a liquid containing the metal complex and drying it to form a metal oxide film on the substrate.

12. The method for forming a film according to claim 1 or claim 2, wherein the metal complex is contained in the liquid raw material.

13. The method for forming a film according to claim 1 or claim 2, wherein the raw material comprises gallium.

14. The aforementioned metal complex is contained in the liquid raw material, The method for forming a film according to claim 1 or claim 2, wherein the raw material comprises a p-type dopant.

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